One of the recent uses of wireless networks has been location identification. Increasing number of mobile service providers are implementing the capability to locate mobile phones within their wireless networks. Mobile service providers use this capability to provide certain functionality to their subscribers, such as E911, or to enhance the experience of a subscriber when using a particular application.
Several different techniques have been used in order to locate mobile phones within wireless networks. High accuracy positioning methods, which provide better location identification, form one group of technologies. Time difference of arrival (TDOA) and Enhanced Observed Time Difference (E-OTD) location determination is based on the slight delays caused by the distance differences between the subscriber and the different antennas. These methods compare differences in arrival times of wireless signals between at least 3 different antennas to make the location determination. Assisted GPS (A-GPS) is another technology which can be used for high accuracy location identification. A GPS transceiver, attached to or integrated in the subscriber device, is used to determine the phone's coordinates. This is done in cooperation with the base stations. There is also a low accuracy method in use, generally known as the Cell-ID method. This method relies on the fact that in a wireless cell network, each location is served by a discrete cell. Thus, the location of a mobile subscriber can be determined when a mobile subscriber enters an area served by a particular cell.
High accuracy location identification systems are generally expensive to install, slow to deliver locations and which involve a discrete user request to locate, from an operator. A typical E-OTD installation may require software upgrades to the network, the addition of E-OTD chips to the user devices, and the addit of a hardware component to the network's base stations. TDOA doesn't require any modifications to the handset, but in a typical setup, equipment has to be added to tens of thousands of base stations. These methods also typically entail “assistance” from the operator, and hence may involve a charge for doing individual location identification. Moreover, since information is usually communicated to the base stations, there is also additional power drainage from the handsets. Low accuracy systems, on the other hand, can suffer from poor precision. The precision of the coordinate identification depends on the size of the cell; the larger the cell size, the poorer the precision.
These limitations make the use of these systems impractical for “location-aware” applications that run in the background. These applications, which need to continually identify a subscriber's location, need a methodology which will enable location identification inexpensively, and without user intervention. Moreover, these location identifications should be done with greater accuracy then typically provided by the Cell-ID method, though the precision of the high accuracy methods is not needed.